Electroluminescent display

• US 5,416,494 A
• Filed: 12/23/1992
• Issued: 05/16/1995
• Est. Priority Date: 12/24/1991
• Status: Expired due to Term

• Current Assignee: Nippondenso Co., Ltd. (DENSO Corporation)
• Original Assignee: Nippondenso Co., Ltd. (DENSO Corporation)
• Inventors: Matsumoto, Muneaki, Osada, Masahiko, Yokota, Minoru
• Primary Examiner(s): Oberley, Alvin E.
• Assistant Examiner(s): Saras, Steven J.
• Application Number:
  US07/997,310
• Time in Patent Office: 874 Days
• Field of Search: 340/701, 340/805, 340/704, 313/500-509, 345/76-81, 345/4, 345/209, 315/169.3
• US Class Current: 345/79
• CPC Class Codes: G09G 2300/023 Display panel composed of stacked panels
• CPC Class Codes: G09G 3/12 using electroluminescent elements
• CPC Class Codes: G09G 3/30 using electroluminescent panels
• CPC Class Codes: H05B 33/12 Light sources with substantially two-dimensional radiating surfaces

Abstract

An EL display includes first and second EL elements each having an EL photoemissive layer and a pair of electrodes provided on opposite surfaces of the EL photoemissive layer. The EL photoemissive layer of each of the first and second EL elements is enabled to emit light when a voltage applied between the electrodes of the EL element is equal to or greater than a given threshold value. A voltage feed circuit serves to apply a first ac voltage between the electrodes of the first EL element. The first ac voltage has a value being equal to or greater than the threshold value. The voltage feed circuit also serves to apply a second ac voltage between the electrodes of the second EL element in cases where photoemission of the second EL element is required. The second ac voltage has a value equal to or greater than the threshold value. The second ac voltage has a phase different from a phase of the first ac voltage. Furthermore, the voltage feed circuit serves to apply a third ac voltage between the electrodes of the second EL element in cases where photoemission of the second EL element is not required. The third ac voltage has a value smaller than the threshold value. The third ac voltage has a phase different from the phase of the first ac voltage.

Claims

1. An EL display comprising:

a first EL element and a second EL element, wherein each EL element includes;

a pair of electrodes; and

an EL photoemissive layer disposed between the electrodes, wherein the EL photoemissive layer is capable of emitting light when a voltage applied between the electrodes is equal to or greater than a threshold value; and

voltage feed means for applying a first ac voltage between the electrodes of the first EL element, and for applying a second ac voltage between the electrodes of the second EL element at the same time as the application of the first ac voltage, wherein the first ac voltage has a value which is equal to or greater than the threshold value, wherein the second ac voltage has a polarity which is opposite to a polarity of the first ac voltage so that the application of the second ac voltage at the same time as the application of the first ac voltage enhances a noise suppression effect, wherein the second ac voltage has a value which is equal to or greater than the threshold value when photoemission of the second EL element is required, and wherein the second ac voltage has a value which is smaller than the threshold value when photoemission of the second EL element is not required.

2. The EL display of claim 1, wherein the first EL element and the second EL elements are arranged in a laminated structure.

3. The EL display of claim 2, wherein one of the electrodes of the first EL element and one of the electrodes of the second EL element are comprised of a common electrode.

4. The EL display of claim 1, wherein the first EL element and the second EL element are disposed adjacent to each other in a common plane.

5. The EL display of claim 4, wherein one of the electrodes of the first EL element and one of the electrodes of the second EL element are comprised of a common electrode.

6. The EL display of claim 4, wherein one of the electrodes of the first EL element and one of the electrodes of the second EL element are comprised of a common electrode, and the EL photoemissive layer of the first EL element and the EL photoemissive layer of the second EL element are comprised of a common EL photoemissive layer.

7. The EL display of claim 5, wherein the common electrode is in an open state, and one of the first ac and voltage second ac voltage has a value equal to or greater than twice the threshold value.

8. The EL display of claim 6, wherein the common electrode is in an open state, and one of the first ac voltage and the second ac voltage has a value equal to or greater than twice the threshold value.

9. The EL display of claim 4, further comprising at least a third EL element, and wherein the first EL element, the second EL element and the at least a third EL element are arranged in a matrix, and wherein the voltage feed means comprises means for scanning the matrix while applying ac voltages thereto.

10. The EL display of claim 1, further comprising:

a first insulating layer disposed between one of the electrodes and the EL photoemissive layer in the first EL element and the second EL element; and

a second insulating layer disposed between the other electrode and the EL photoemissive layer in the first EL element and the second EL element.

11. The EL display of claim 1, wherein the first ac voltage and the second ac voltage each have rectangular waveforms.

12. The EL display of claim 1, further comprising:

an even number of additional EL elements, and wherein the voltage feed means comprises means for applying first-type ac voltages between the electrodes of half of the additional EL elements, and for applying second-type ac voltages between the electrodes of the other half of the additional EL elements, wherein the first-type ac voltages have a polarity opposite to a polarity of the second-type ac voltages.

13. An EL display comprising:

a plurality of EL elements, each disposed so as to be capable of indicating either of preset characters, wherein each of the EL elements is capable of emitting light when a voltage having an absolute value which is equal to or greater than a threshold value is applied thereto, and wherein the EL elements include at least a first EL element and a second EL element;

means for feeding a first ac drive voltage to the first EL element so as to activate the first EL element, wherein the first ac drive voltage have a value which is equal to or greater than the threshold value; and

means for feeding a second ac drive voltage to the second EL element, at the same time the first ac drive voltage is fed to the first EL element, so as to activate the second EL element at the same time the first EL element is activated, wherein the second ac drive voltage have a value which is equal to or greater than the threshold value, and wherein the second ac drive voltage have a polarity which is opposite to a polarity of the first ac drive voltage.

14. The EL display of claim 13, wherein the EL elements further includes at least a third EL element, and wherein the EL display further comprises:

means for feeding a third ac voltage to the third EL element, at the same time first ac drive voltage is fed to the first EL element and at the same time the second ac drive voltage is fed to the second EL element, so as to enhance a noise suppression effect, wherein the third ac voltage have a value which is smaller than the threshold value, wherein the third ac voltage have a polarity which is opposite to one of the polarities of the first ac drive voltage and the second ac drive voltage, and wherein the third EL element is disposed adjacent to one of the first EL element and the second EL element.

15. An EL display comprising:

an EL photoemissive layer which is capable of emitting light when a voltage having an absolute value equal to or greater than a threshold value is applied thereto, wherein the EL photoemissive layer has a first surface and a second surface;

a plurality of scanning electrodes disposed on the first surface, wherein the scanning electrodes are disposed so as to be parallel to each other;

a plurality of data electrodes disposed on the second surface, wherein the data electrodes are disposed so as to be parallel to each other;

scanning-electrode voltage feed means for sequentially feeding a scanning voltage to the scanning electrodes and for sequentially feeding an anti-phase voltage to the scanning electrodes, wherein the scanning voltage has an absolute value which is smaller than the threshold value, wherein the anti-phase voltage has an absolute value smaller than the threshold value, wherein the scanning voltage and the anti-phase voltage are fed, at the same time, to different scanning electrodes and wherein the anti-phase voltage has a polarity which is opposite to a polarity of the scanning voltage; and

data-electrode voltage feed means for feeding, at the same time the scanning voltage is fed to the scanning electrodes, a data voltage to a selected one of the data electrodes, wherein the data voltage has an absolute value which is smaller than the threshold value, wherein the absolute value of the data voltage is greater than the threshold value minus the scanning voltage, and wherein the data voltage has a polarity which is opposite to the polarity of the scanning voltage; and

wherein the scanning-electrode voltage feed means feeds the scanning voltage and the anti-phase voltage to adjacent pairs of the scanning electrodes so as to enhance a noise suppression effect.

16. An EL display comprising:

a first EL photoemissive layer having an axis related to piezoelectricity;

a second EL photoemissive layer having an axis related to piezoelectricity,. wherein the first EL photoemissive layer and the second EL photoemissive layer are disposed so as to be adjacent to each other;

first means for generating an ac voltage;

second means for applying a first ac electric field to the first EL photoemissive layer so as to activate the first EL photoemissive layer in response to the ac voltage generated by the first means; and

third means for applying a second ac electric field to the second EL photoemissive layer so as to activate the second EL photoemissive layer in response to the ac voltage generated by the first means, wherein the third means applies the second ac electric field simultaneously with the application of the first ac electric field by the second means, and wherein a direction of the first ac electric field relative to the piezoelectricity-related axis of the first EL photoemissive layer is substantially antiparallel to a direction of the second ac electric field relative to the piezoelectricity-related axis of the second EL photoemissive layer.

17. An EL display comprising:

a first EL photoemissive layer having an axis related to piezoelectricity;

a second EL photoemissive layer having an axis related to piezoelectricity, wherein the first EL photoemissive layer and the second EL photoemissive layer are disposed so as to be adjacent to each other;

first means for generating a first ac voltage having a first polarity;

second means for applying a first ac electric field to the first EL photoemissive layer so as to activate the first EL photoemissive layer in response to the first ac voltage generated by the first means;

third means for generating a second ac voltage having a second polarity, wherein the second polarity is equal to the first polarity; and

fourth means for applying a second ac electric field to the second EL photoemissive layer so as to activate the second EL photoemissive layer in response to the second ac voltage generated by the third means, wherein the fourth means applies the second ac electric field simultaneously with the application of the first ac electric field by the second means, and wherein a direction of the first ac electric field relative to the piezoelectricity-related axis of the first EL photoemissive layer is substantially antiparallel to a direction of the second ac electric field relative to the piezoelectricity-related axis of the second EL photoemissive layer.

18. The EL display of claim 17, wherein the first ac voltage and the second ac voltage each comprise a common ac voltage.